They are not supposed to sell their addons. They can have a donation button, but they can’t require it to use the addon.
Addon managers are a completely different beast. The addon manager can be a premium service that you use to conveniently install things instead of doing it manually.
The rules on paying individual creators though … I don’t know how that legally works, unless they just get a cut of whatever fees are paid to the addon manager.
I manually handle my own addons though so it does not impact me.